DC power supplies powered by the AC mains, for use in powering portable electronic devices such as mobile phones, laptop computers, or to charge batteries such as are known popularly as wall chargers or adaptors, or travel converters, are possibly the most common power supplies in use today. Such power supplies, if of the “high efficiency” type, generally use a rectifier bridge, with a capacitor output for reservoir and smoothing purposes, feeding a DC/DC converter of the switched mode type, generally a pulse width modulation (PWM) power supply, also capacitor smoothed at its output, to generate a regulated, low voltage DC output. Although the efficiency of such power supplies is high compared with previously available linear regulated power supplies, there has recently been a tendency, related to concern for the environment, to increase efficiencies even more, and especially to reduce the standby dissipation of the units when they are connected to the mains supply but are not delivering current to a load.
There exists a constant need for a power supply which increases still further the wall-plug efficiency and reduces the standby power consumption compared with prior art power supplies.
The disclosures of each of the publications mentioned in this section and in other sections of the specification, are hereby incorporated by reference, each in its entirety.